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People diagnosed with HIV who have a recent history of Truvada (tenofovir disoproxil fumarate/emtricitabine) as pre-exposure prophylaxis (PrEP) use are much more likely than HIV-diagnosed people who have never used PrEP to have viral mutations conferring resistance to the emtricitabine component of the two-drug combination antiretroviral (ARV) tablet.

Researchers are concerned that people who start taking PrEP while they have HIV may develop resistance to either of the drugs in Truvada. The two drugs in the tablet are insufficient to properly suppress a chronic HIV infection; at least one other ARV is required for a complete treatment regimen. Consequently, someone who has HIV and takes PrEP may see their virus replicate at a high enough level to develop resistance to the virus.

If someone starting PrEP was not tested for HIV prior to receiving a prescription for Truvada or if he or she is so recently infected that an HIV test yields a false negative result, the individual may wind up taking Truvada in the face of a chronic infection with the virus.

Kavita Misra, PhD, MPH, of the New York City Department of Health and Mental Hygiene, presented findings from the new study at the 2019 Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle. She and her colleagues analyzed data on the 3,685 individuals who had been diagnosed with HIV in New York City within the previous 12 months and were assigned to what is known as partner services between November 2015 and August 2017.

Partner services is a process through which people newly diagnosed with the virus help clinicians and public health workers identify their sex or needle-sharing partners.

Ninety-one members of the cohort (2 percent) had a recent history of PrEP use that predated their HIV diagnosis. A median 250 days passed between the time these individuals first received PrEP and their diagnosis.

The study authors analyzed drug resistance testing of the cohort members’ HIV to determine whether they had resistance mutations to either of the ARVs in PrEP: emtricitabine (specifically the mutations known as M184I, V, IV and MV) and tenofovir disoproxil fumarate (specifically the K65R mutation).

There were data on the genotypes of HIV for 75 percent of the PrEP users and 63 percent of those who had never used PrEP. Twenty-nine percent of the PrEP users had any of four mutations that confer resistance to emtricitabine, compared with 2 percent of those who had not used Truvada for prevention. Four people, none of whom had used PrEP, had K65R mutations conferring resistance to tenofovir disoproxil fumarate.

Thirty-three percent of those who had used PrEP had a negative nucleic acid amplification test (NAAT), or viral load test, before their diagnosis, compared with 4 percent of those who didn’t use PrEP. A negative NAAT result indicates a very recent infection. The respective proportions of these two groups who were consdidered to have been diagnosed with HIV during the acute, or very early, phase of infection were 33 percent and 9 percent.

The study authors theorized that the higher rate among the PrEP users of infections diagnosed during the acute phase may have been driven by a higher rate of use of health care services among those with a history of Truvada use.

The overall findings underline the importance of conducting proper screening among those seeking PrEP to reduce the chances that people will start Truvada when they have undiagnosed HIV.